Present day production level uranium enrichment, i.e. separation of the U-235 isotope, is achieved by what is commonly known as the gaseous diffusion technique. According to known aspects of this technique, molecules of uranium hexafluoride (UF.sub.6) are forced under pressure through sets of small holes or channels in a diffusion screen which constricts the flow of the uranium hexafluoride gas and very slightly affects its flow rate in accordance with molecular weight. Thus the flow rate through the channels will be a function of isotope type permitting a small, typically 0.2% enrichment per stage. The enrichment is typically improved by cascading several stages using both feedback and feedforward systems between waste and product streams respectively.
The very small mass difference between the atoms of different isotope types making up the uranium hexafluoride molecule and even smaller total relative mass difference between the complete molecules places a limit upon the difference in diffusion rates which may be achieved for the isotopically distinct molecules. This limit is, as indicated above, very small and necessitates the cascading of many stages of diffusion channels if uranium is to be enriched from its naturally occurring concentration of about 0.7% up to approximately 2-4% for typical use in power generating reactors.
A wholly different approach to uranium enrichment is described in U.S. Pat. No. 3,772,519 which utilizes differences in radiation absorption frequency between isotope types, particularly of elemental uranium, to permit ionization of particles of one isotope type so that a separation may be created electrically.